Power hydraulic brake device and system



May 28, 1963 R. E. scHwAR-rz ETAL 3,091,086

PowER HYDRAULIC BRAKE DEVICE AND SYSTEM original Filed March 28, 19555 2Sheets-Sheet 1 May 28, 1963 POWER HYDRAULIC BRAKE DEVICE AND SYSTEMOriginal Filed March 28, 1955 z'sheets-sheet 2 INVENTORS ROBERT E.SCHWARTZ ATTORNEYS l 3,091,986 PWER HYDRAULEC BRAKE DEVHCE AND SYSTEMRobert E. Schwartz, Clayton, Mo., Roy P. Stahl, South Bend, 1nd., andEdward J. Falk, St. Louis, Mo., assignors to Wagner ElectricCorporation, St. Louis, Mo., a corporation of Delaware Appiication Mar.15, 1960, Ser. No. 15,221, now Paten No. 3,044,255, dated July 17, 1962,which is a continuation of application Ser. No. 497,272, Mar. 28, 1955.Divided and this appiication Nov. 3, 1961, Ser. No. 150,080

Claims. (Cl. Sil-54.6)

This invention relates to power hydraulic systems and the controllingmeans therefor, and in particular, to a power brake system and servomotor utilizing sepa-rate power hydrau-lic pressure iiuid 'and brakeiiuid.

In general, this invention comprises an operator controlled servo motorserially arranged with positive displacement pumping means .in a powerhydraulic system for the actuation of a brake system. It -is well-knownin the industry that a mineral base pressure fluid is preferable as apower hydraulic fluid, but that the best materials known for sealingmembers land like resilient components for `a brake device are `attackedby such uid .and have a relatively short life. Accordingly, the bestpower fluid is not compatible with :the best pressure producing duid forbrake actuation, and in the past .a compromise uid has generally beenutilized because of the rapid seal deterioration and dilution of onepressure -uid by the other when attempts have been made to use separatepower and actuation iluids. However, because of the improved uidoperating characteristics produced by using separate power hydraulicpressure fluid and brake flu-id, it is advantageous land desirable toprovide an cimproved servo motor having isolated power and brakeactuating portions.

One of the principal objects of the present invention is to provide yaservo rnotor which completely separates the fluid in the series powerhydraulic portion of the system from the fluid in the braking portion ofthe system.

Another object of the present invention is `to provide a braking systemoperated by a servo motor in series with a power system, but whichfunctions 4independently of the ambient pressure in any section of thepower system.

Still another object of the presen-t invention is to provide a servomotor which provides feel for the operator. Feel is the proportionalreactionary force in opposition to the applied force aifording theoperator an appraisal -as to the extent of application.

Another object of the present invention is to provide a servo motorwhich operates even in the event of power failure to provide safeoperation of the braking system.

A still further object is to provide a servo motor having novel pressureiluid compensation means for a brake cylinder portion thereof.

The invention also consists -in the parts and in the arrangements andcombinations `of parts hereinafter described and claimed. In the'accompanying drawings which form part of this specification and whereinlike numerals and symbols refer to like parts wherever they occur:

FIG. 1 is a diagrammatic view of a power hydraulic braking system with alongitudinal cross-sectional view of the power hydraulic brake deviceshown therein,

FIG. 2 is a fragmentary cross-sectional view showing the compensationvalve `of the preferred embodiment in detail,

FIG. 3 is ya greatly enlarged fragmentary view of the ilow throttlingportion of the power hydraulic brake device shown in FIG. 1, and

FIG. 4 is :a cross-sectional view taken along line 4-4 in FIG. 3.

fice

This is a division of copending application, Serial No. 15,221 filedMarch l5, 1960, now Paten-t No. 3,044,265, for Power Hydraulic BrakeDevice and System, which application is a continuation of ourapplication Serial No. 497,272, tiled March 28, 1955, vnow abandoned,ttor Power Hydraulic Brake Device and System.

Referring to FIGS. l, 3 and 4, the power hydraulic system comprises :apumping means 1 having one side connected to a reservoir 2 -by a conduit3 and the pressure side connected to the inlet of the power portion of aservo motor 4 yby a conduit 5. A conduit 6 connects the outlet of thepower portion of the servo motor 4 with a power steering valve 7arranged in series with said servo motor 4. The outlet of the steeringvalve 7 is connected to the reservoir 2 by a conduit 8 which provides areturn passage for the oil displaced by the pumpling means 1. A conduit9 having `a pressure relief valve 10 interposed therein connects 'theconduits 3 and 5, the relief -valve -10 protecting the pumping means 1from pressure overload 'above ya predetermined value. A conduit 11connects the conduits 6 and S and has 'a reverse -flow valve 12interposed therein to facilitate pressure fluid recirculation during apower failure steering application. If desired, the valve 12 may beintegral with the power steering valve 7. The braking system includes aplurality of wheel cylinders 13 connected to Ithe brake actuatingportion `of the servo motor by a conduit 14. A conduit 15 connects abrake fluid reservoir 16 to the servo motor for compensation purposes.According to the present invention, the power system contains a mineraloil .base pressure uid and the braking system contains a typicalhydraulic brake fluid.

The servo motor 4 comprises a booster housing 17 having a brake portionhousing 1S secured to the righthand end `and defining :a pressureproducing outlet cham- 1 er `or master cylinder .chamber C, and yanintake housing 19 secured to the leftehand end of the booster housing 17:and deiining .therewith a power portion of the servo motor 4. The powerportion includes an inlet chamber A and an `outlet or ret-urn chamber Bas will be more ffully -dened hereinafter. The intake housing 19 has arod :receiving bore y29 with ya sealing assembly 21 supported thereinand an axially aligned counterbore 22. The counterbore 22 receives aleftward extension of the booster housing 17 which has a counterbore 23therein, `the extension supporting an -O ring 22' which seals between-the booster housing 17 and the counterbore 22. The intake housing 19.also has a vertically disposed inlet 24 to which the conduit 5 from thepumping means 1 is connected and which connects with the inlet chamberA. A return port or outlet 25 connects with lthe reservoir chamber Bdened in part by the counterbore 23 in the booster housing .17. A sleevetype pressure relief valve 26 is interposed between the inlet 24 vandoutlet 25 and is received in a connecting passage formed by ahorizontally disposed bore 27 and an laxially laligned counterbore 28,the valve 26 being biased against a seat 29 by a spring 30 whichcircumscribes @a guide extension 31 of the valve 26. The righ-t end ofthe spring 30 .abuts against a compression adjusting spacer 32interposed between the spring 30 and the right end of the counterbore28. An =0 ring 27 provides .a seal between the housing `17 and 19circumscribing the bore -27 and .the counter-bore 28. The pressurerelief valve 26 is provided in by-pass relation with the power chambersA rand B and is biased by the predetermined force of the spring 30 intonormally sealed position with the seat 29. However, power hydraulicpressures developed in the inlet chamber A by power control meansincluding a piston rod 33 and a .-throttling valve 39 for :actuating apower piston 41 to develop braking pressures in the pressure producingchamber C may act .on the eitective area of the valve 26 to of the powerpiston 41.

3 overcome the force .of spring 30 in order to prevent overloading thepumping means 1.

The piston rod 33 includes a leftward portion 33 slidably mounted in thebore 20 and receiving a linkage 34 pivotally mounted between the rod -33and one end oi a push -rod 35. The other end of the push rod 35 isoperatively connected with suitable `actuating means such kas an.actuating pedal 36 having intermediate Linkage (not shown) interposedtherebetween. A resi-lient, boot 37 interposed ybetween the push rod 35and the intake bousing 19 prevents the entry of lforeign materials, butthe effective area of the portion 33 to the left of the seal 21 issubjected to atmospheric pressure.

The rod 33 extends coaxially into a counterbore 38 of la leftward sleeveportionr38 of the throttlin-g valve 39 land is spaced therefrom by aplurality of ears 40 to provide an annular passage 40 in communicationWith the inlet cham-berA. The right end of the rod 33 is secured to thevalve 39. The power piston 41 is slidably positioned in the counter-bore23 and -divides the power chamber into the inlet and outlet chambers Aand B. The pistonr41 includes an inner bore 42, an intermediate bore 43,and an outer bore 44. The valve 39 is positioned in the outer bore 44and has a radially-extending 'annular fange 45 therein and the valve 39also includes a rightw-ard portion 39 extending linto the intermediatebore 43 A plurality of angularly arranged passages 46 are formed in thevalve 39 connecting the couuterbore 38 with the outer lbore 44, and theouter Vcircumferential portion at the left end of piston 41 Vhavin g aplurality of throttling passages 47 providing communication between theouter bore 44 and the chamber B. The passages 47 zform Ia throttlingpassage D in combinartion with fthe radial ange 45 of the throttlingvalve 39.

A seal assembly 48 is provided inthe outer bore 44 between the Ibore 44andthe periphery of lthe rightward portion 39 of the valve 39. Therightward portion 39 andthe leftward portion 33 of .the piston 33 havethe same diameters and therefore have the same Ieffective end areasoutwardly of the seals 48 :and 21, respectively. In order to provide abalanced power piston arrangement as taught herein, it is necessary tosubject these efective areas to the .same surrounding or ambientpressure which in `this case is atmospheric. A spring 49 of negligibleforce is mounted in the inner bore `42 biasing the radial Yange 45 ofthe valve 39 leftwardly to its open or unstricting .but not closing thepassage D. In :both positions,

the leftward side of the radial ilange 45 is subjected to the same fluidpressure that prevails `in return chamber B and 'the rightward side ofthe flange 45 is :subjected to chamber A fluid pressures. The opposedeffective areas vof the piston rod 33 and throttling valve 39 betweenthe seals 21 land 48 are equal.

The valve'39 carries a seal assembly 51 which extends into sealedcondi-tion fwith the lcounterb'ore k23 at the left VVendV of the piston41 and seals between the chambers A and B, the seal assembly 51 having:a retainer member to keep the sealing cup in sealing position. Theretainer :acts as la stop member ttor the piston rod 33 and throttling'Valve 39 :against :the left end of the intake bore 22, and is alsopenforated Vtor the free passage of power hydraulic fluid. The oppositeelective 'areas of the power piston 41-in chambers A and B land acrossthe sealing cup 51 are equal. Another sealing assembly 52 isfpositionedin the end lof the counterbore 23 and lprovides a seal 'around thepiston 41, the seal 52 and each of the other seals inthe power portionofthe servo motor being of a material adapted -for long life with mineraloil base power uid.

Al fluid separation counterbore or chamber 53 is axially 4 aligned withthe counterbore Z3 and is in communication with the inner bore l42 ofthe piston 41 :by means of a passage 54, the passage Ibein-g an escapefor any pressure iluid which might leak past thesealing assembly 48. Apassage 55 having anxair lter 56 is vertically disposed in the boosterhousing 17 in communication with the separation chamber 53 and the leftend thereof Iand-provides a drain for any uids which might collect insaid counterbore 53. It is apparent that the ri-ghtwalrd portion 39' ofthe -thro-ttling valve 39 is subjected to atmospheric pressure to oisetor balance the equal and opposite force on the leftward end of theportion 33 tof the piston rod 33. It is :also Iapparent that atmosphericpressure acts on the effective area of the power piston 41 in the 'bore42 and this yarea is Vbalanced by yan equal effective area orf thepiston 41 in the separation chamber 53 outwardly ofthe seal 52.

The ybrake housing 18 partially extends -into the vcounterbore 53 havingla bore 57 which defines the outlet chamber C :at the right end thereof,and which -slidably receives v'a master ycylinder portion 58 which isretained therein :by suitable means. The piston 58 has a leftward sleeveor annular projection l59 with a long recess or bore 60 to receive yanextension I61 of the power piston 41. The :extension 61 and sleeve l60have yan :axial extent of sucient length to assure rectilinearlactuation of the piston 58 in the chamber C. lI-t is apparent that thepistons 41 land 58 may be integral so thatthe power piston has anextension with la piston working end in the outlet chamber C. Aresilient boot 62 -is interposed .between the 4sleeve 59 :and the brakefhousing V18 in circumsc-ribing relation therewith and prevents theentry Iof foreign matrter. An annular spacer 63 is positioned againstthe right end wall 80 of the counterbore 53, 'and a spring 64 extendsfrom the spacer against ya retainerS carried by the extension 61 andinterposed in a step 79 formed between adjacent vertical walls of thepistons 41 zand58. The spring 64 is of negligible torce only greatenough to bias the retainer 65 against theleft end-wall 81 of theseparation chamber 53 adjacent to the power portion of the servo motor 4:for returning the power piston 41 to inoperative or retracted position.The retainer 65 may function as ya deflector or drip guard to prevent oworf any power hydraulic fluid seeping past seal 52 from migrating alongthe piston sleeve 59.

A primary seal 66 is provided in chamber C Yfor the working end ofthepiston 58 and a spring and retainer assembly 67 biases the seal I66 intoan abutting relationshipwith the piston 58. The sleeve 59 also carries asecondary seal 68 in sealing contact with the bore 57, the seal 68 beingformed of a material to seal brake uid. It is apparent from FIG. 1 thatthe separation chamber 53 has an axial extent greater than the maximumstroke of the pistons 411 and 58, and'that the piston surfaces sealed bysealing assemblies 52V and 68 are never in contact with other surfaceswhereby transfer-of power and brake fluids is prevented.

A reservoir port 69 is vertically disposed in the brake housinglS forcompensation, purposes. One end ofthe port 69 receives the conduit 15and the other end 69' intersects the bore 57 adjacent tothe lip of theseal'66 Ain its normal inoperative position. In FIG. 2, a compensationvalve 70 is biased by -a spring 71 into a seat 72 formed by the junctureof a bore 73 and an axially aligned `counterbore 74 horizontallydisposed in thebrake housing 18, the right end of said spring 71abutting against anend plug 75 tixedly received in the counterbore 74.The left end of the bore 73 is connected to the reservoir port 69 by across-drilled passageway 76. Another cross-drilled passage 77 isprovided in the brake housing 18, one end thereof intersecting thecounterbore 74, the mid-portion thereof being in communication vwith thebore 57, and the other end forming a brake port 78. The brake port 78receives the conduit 14, FIG l1, con necting the bore 57 with the brakeassemblies. v

In this series system, the pressure relief valve actuates at a pressureequal to the sum of the maximum pressure differentials allowed acrossthe individual servo motors thereby protecting the pumping means 1 frompressure overloads. Pressure overloading of the pumping means 1 developswhen the servo motor 4, or other servo motors of `other devices such assteering valve 7, exceeds the predetermined maximum pressuredifferential assigned thereto. The servo motor 4 is provided with apressure relief valve 26 which limits the magnitude of the maximumpressure diiferential allowed thereacross. However, the fluid pressureexisting in a servo motor at any time is effective upon every servomotor of prior position in the system. For instance, if the steeringvalve 7 is actuated, the pressure differential created thereacrosscauses a back pressure which is effective throughout the servo motor 4and against which the pumping means 1 must work. Ordinarily, a servomotor of prior position would be actuated by this back pressure.However, the servo motor 4 is balanced to prevent such an occurrence,this balancing being achieved by a symmetry of crosssectional areaswhich are affected by the aforesaid back pressure. The opposingeffective cross-sectional areas of the piston y41, the valve 39, and thevalve rod 33, respectively, are constructed to be equal andself-cancelling when acted upon by the ambient uid pressure existing inthat particular section of the hydraulic system. Atmospheric pressure isalso prevalent acting upon opposing effective cross-sectional areas ofthe piston 41, and the valve 39 and the valve rod 33. However, theforces thus created are also equal and self-cancelling. Consequently,regardless of the ambient pressure the servo motor 4 is balanced tofunction independently in the series system.

Assuming the steering valve to be unrestricted, pressure iluid isnormally discharged from the pumping means 1 through the conduit 5 andthe inlet 24 into the inlet chamber A of the servo motor 4. As shown bythe ilow directional arrows in FIG. 3, the pressure uid then ows betweenthe valve rod 33 and the valve 39 through passage 4G' and through thepassages 46, the outer bore 44, and the normally unrestricted throttlingpassages 47 into the outlet chamber B. Prom the outlet chamber B thefluid flows by means of the outlet 25 and the conduit 6 into the powersteering valve 7 and is returned to the reservoir 2 through the conduit8.

When the vehicle operator applies a force to the actuating pedal 36, athrottling rforce is transmitted to the push rod 35, the linkage 34, thevalve rod 33 and the throttling valve 39 which is moved rightwardlyrestricting pressure fluid ilow through the throttling channel D betweenthe flange l45 and the right end of the throttling passages 47.Consequently, a pressure differential is created across the power piston41 between the chamber B and the portion of the outer bore 44 of thepiston 41 between the piston and the throttling valve flange 45 todevelop a back pressure against which the pumping means 1 must work. Thepressure differential also exists across the sealing cup `51 between thechamber A and the portion of the bore 44 between the seal 51 and theleft side of the throttling valve flange 45. In effect, the pressuredifferential across the piston 41 exists in the chambers A and B, andthis pressure differential is also exerted as a reactionary force on thethrottling valve flange 45 in opposition to the actuating force therebyproviding feel. Because of the existing pressure differential betweenchambers A and B, the piston 41 moves rightwardly compressing the spring64 in the separating counterbore 53 and actuating the piston 58 and theseal 66 further into the outlet chamber C to develop brake pressures inthe wheel cylinders A13. The valve 39 and valve rod 33 are maintained ina restricted, but not closed, position relative to the piston 41 by themanually applied force in opposition to the pressure of the power fluidacting on the rightward side of the radial flange 45 of 6 the throttlingvalve 39 in order to continue the braking application. This movementdisplaces brake iluid from the pressure producing chamber C through thebrake port 78 and the conduit 14 into the wheel cylinders 1'3 therebyactuating the brake assemblies. The brake fluid pressure developed inthe chamber C acts on the effective area of the seal 66 creating areactionary force in opposition to the motivating force of the piston41. When the reactionary force equals the motivating force, the right-Ward movement of said piston 41 ceases. In the above described case, theoperator is afforded a feel as to the extent of the braking applicationin that he feels the created pressure differential on the effectiveareas of the valve rod 33 and the valve 39 which is directlyproportional to the hydraulic output to the wheel cylinders 1'3.

When the operator releases the applied force, the established fluidpressure in the bore 57, the spring 64, and the spring 67 returns thepiston 41, the piston 5S, and parts associated therewith to their normalpositions. When this occurs, a partial vacuum is developed in the bore57, and the pressure differential across the valve 70 opens the valveallowing brake uid to compensate into the bore 57. Therefore, the vacuumcreated in the bore 57 is overcome and any excess uid present when thewheel cylinders are in inoperative position is returned to the reservoirline 15 through port 69.

In the event of power failure, the operator is required to supply allthe actuating force in operating the servo motor 4. As previouslydescribed, the force applied by the operator motivates the valve 37rightwardly. Due to the absence of pressure fluid circulation throughthe throttling passages 47, restriction of the passage D does notdevelop a pressure differential to motivate the power piston 41.Consequently, the right end of the valve 39 abuts against the powerpiston 41 and carries the piston 41 and the piston 53 rightwardly. Uponthis n'ghtward movement, the lip of the sealing cup in the sealingassembly 51 will collapse allowing the pressure fluid to flow thereby.Therefore, the use of a reverse flow valve allowing pressure fluidrecirculation is obviated. This rightward movement also displaces brakefluid from the outlet chamber C through the brake port 78 and the con--duit 14 into the wheel cylinder assemblies 13 to actuate the brakeassemblies. Upon release of the applied force, the brake iluid pressurein the bore 57 and the cornpressive force of the springs 64, 67 and 49return the power piston 41, the piston 58, the valve rod 33 and partsassociated therewith to their normal position.

The construction of the servo motor 4 completely isolates the oil basedpressure fluid used in the power hydraulic system from the brake fluidemployed in the braking system. Any oil based pressure fluid leakingpast the sealing assembly 48 in the power piston 41 will ilow throughthe passage 54 into the separation chamber 53, and any pressure fluidleaking past the sealing assembly 52 flows directly into the chamber 53.Therefore, any pressure uid collecting in the separating counterbore 53will drain therefrom through the passage 55. The braking system isprotected from the entry of pressure uid thereinto by the boot 62 in thecounterbore 53. If any brake fluid escapes past the secondary seal 68,it will collect in the boot 62. However, if said boot 62 should rupture,the brake fluid will drain from the counterbore 53 through the passage55 and in any event no transfer of fluids will be effected in continuousoperation of the servo motor without a boot 62 since no seal for onefluid wipes a surface exposed to the other uid. Therefore, the servomotor 4 completely separates the pressure fluid in the power hydraulicsystem from the brake fluid of the braking system.

This invention is intended to cover all changes and modifications of theexample of the invention herein chosen for purposes of the disclosure,which do not constitute departures from the spirit and scope of theinvention.

Yeffect movement of said piston assembly in the work producingdirection, and flange means on said throttling means responsive to theestablished pressure differential to oppose subsequent movement of Ysaidthrottling means Vto reduce the size of said variable orifice.

2. In a power hydraulic servo motor comprising a housing having aborewith a piston assembly therein movable in a work producing direction, avariable orice in said piston assembly through which pressure Huid iscontinuously circulated, and means including ange means movable relativeto said piston assembly in response to an applied force to reduce thesize of said variable orifice and'establish a pressure differential toeffect movement of said piston assembly in the work producing direction,said flange means being responsive to the established pressuredifferential to create a proportional reactive force in opposition tosaid applied force.

3. A hydraulic cylinder comprising a housing having a bore therein,piston means slidable in said bore, expansible chambers in said bore onopposite sides of said piston means, throttling valve means normallyjuxtaposed with said piston means, flange means on said throttling valvemeans, normally unrestricted, but variable, passage means formed betweensaid throttling valveand piston means and connecting with said chambers,means for continuously circulating pressure fluid through said passagemeans -and chambers, means for moving said throttling valve meansrelative to said piston means to reduce the size of said passage meansand effect a pressure differential across said piston means, thedeveloped pressure differential acting to energize said piston means andacting on said flange means to oppose subsequent movement of saidthrottling means.

r4. A hydraulic servo motor comprising a housing having aligned borestherein, piston means slidable in one of said bores, extension means onsaid piston means slidable in the other of said bores to generate fluidpressure therein, expansible Vchambers in said one bore adjacent theopposed faces of said `piston means, throttling valve means slidable insaid piston means, ange means on said throttling valve means, normallyunrestricted, but variable, passage means formed between saidYthrottling valve means and piston means and connecting with saidexpansible chambers, means connected with said expansible chambers forcontinuously circulating pressure fluid through said expansible chambersand passage means, and

Vforce applying means connected to move said throttling valve meansrelative to said piston means reducing the Vsize of said passage meansand restricting the circulation of pressure -uid therethrough to developa pressure differential across said piston means wherein the developedpressure differential acts on said piston means to move said pistonmeans and extension means to generate uid pressure in said other 4boreand acts on said iiange means to create a proportional reactive force inopposition to the :torce applying means.

5. A hydraulic cylinder comprising a housing having a bore therein,piston means slidable in said bore and having a work producing endVextending exteriorly of said bore, expansible chambers in said boreadjacent the opposedfaces of said piston means, an atmospheric chamberin said piston, throttling valve means slidable in said piston chamber,ange means on said throttling valve means, a normally unrestrictedthrottling passage formed between said flange and piston means andconnecting with Vsaid expansible bore chambers, means for continuouslycirculating pressure uid through said expan- 8 sible bore chambers andthrottling passage, and means for applying a force to move saidthrottling valve means relative said piston means thereby reducing thesize of said throttling passage and effecting a pressure diiferentialacross Isaid piston means to actuate said piston means and the workproducing end thereof, the developed pressure differential acting onsaid flange means to oppose movement of said last named means.

,ing a bore therein, a piston slidable in said bore and 6. A hydrauliccylinder comprising a housing having ya bore therein, a piston slidablein said bore and having a work producing end extending exteriorly Vofsaid bore, inlet andY outlet chambers in -said bore communicating vwiththe opposed faces of said piston, a chamber in said piston vented toatmosphere, a throttling valve slidable in said piston chamber andhaving an applied force receiving end extending exterior-ly of saidbore,throttling flange means on said throttling valve, athrottling passageformed between said liange means and pist-on and connected with saidinlet and ont-let chambers, means Vfor continuously circulating pressurelluid through said inlet and outlet chambers and throttling passage,said throttling valve being responsive to an applied force to move said-ange means lrelative to :said piston for reducing the size of saidlthrottling passage and effecting a pressure diferential across saidpiston to actuate said piston and Work producing end thereof, thedeveloped pressure differential acting on said flange means inopposition to movement of said throttling valve in response to theapplied force thereon.-

7. A hydraulic servo motor comprising a housing havhaving an Vextensionwith a work producing end extending exteriorly of said bore, said pistonhaving a central lchamber vented to atmosphere, a :throttling valvehaving one end slidable in said chamber a-nd lthe other end extendingexteriorly of said bore, said throttling valve inoluding an annularthrottling flange movable axially relative to said piston and defining athrottling passage therebetween, means biasing said throttling valveaway from said piston to normally maintain said throttling .passage Vinunrestricted condition, inlet and outlet chambers in said bore betweensaid housing and ysaid throttling valve and piston, respectively, :saidinlet and `outlet chambers being connected `to said throttling passage,and means for continuously circulating pressure uid through said inletand outlet chambers and throttling passage, said throttling valve beingmovable relative to said piston by an applied force to reduce `the sizeof said `throttling-passage for creating a pressure diierential across-said piston to actuate the extension exteriorly of the bore, saiddeveloped pressure dierential also acting =on -said annular flange ofsaid throttling valve in opposition to the applied force thereon. v

8. A hydraulic servo motor comprising a housing having aligned borestherein, a piston slidable in one of said bores dividing it intoexpansible rst and second chambers, yan extension on said pistonIextending intoY the other of said bores `and Aadapted for movementtherein to generate fluid pressure, 4a central chamber in said pis-tonvented yto atmosphere, a throttling passage formed in said piston Iincommunication with said second chamber, a throttling valve in said firstchamber having one end slidable in said centra-l chamber of said pistonand the other end thereof positioned exteriorly of said one bore forreceiving an applied force thereon, flange means on said 'throttlingvalve movable relative to said pist-on and including a portioncooperable with .said piston to control the size of said throttlingpassage, resilient means normally biasingsaid throttling valve to aninoperative position and maintaining the flange means portion in anunrestr-icting, inoperative position relative to said piston,

- passage means extending from said rst chamber between with said rstand second chambers, yrespectively, for continuously owing pressurefluid through said irst chamber, passage means, throttling passage andsecond chamber, operator controlled means for applying a force to saidother end of said throttling valve to move said throttling valve to anoperative position relative to said piston with said ange means portionrestricting the size of said throttling passage to develop a pressuredifferential across said piston to move :said piston and extension andgenerate fluid pressure in said other bore, the developed pressuredifieren-tial aiso acting across said flange means to establish aproportional `reactive force in opposition to the force applied by saidoperator controlled means.

9. In .a hydraulic cylinder including piston means slidlable therein`and having opposed faces, throttling means movable relative to saidpiston means in response to an applied force, normally unrestricted, butvariable, passage means formed between said throttling means and pistonmeans interconnecting said opposed piston faces and through whichpressure fluid Iis continuously owed, the combination therewithcomprising `flange means on said throttling means Iand movable therewithrelative to said piston means in response to the applied force into flowrestricting relation with said passage means reducing the size yof saidpassage means and establishing a pressure differential between saidopposed piston faces to effect movement of said piston means, said angemeans being responsive tothe established pressure differential to createa reactionary force in opposition to the applied force to opposesubsequent movement of said throttling means to further reduce the sizeof said passage means.

1-0. A hydraulic cylinder comprising ia piston slidable therein andhaving a work producing end extending exrteriorly lof said cylinder, apair of stepped bores in said piston, expansible inlet and outletchambers in said cylinder adjacent the opposed faces of said piston,normal-ly unrestricted, but variable, oriiice means in said pistonbetween said outlet chamber and `one `of said stepped bores, throttlingmeans slidable in the other of said stepped bores and having flangemeans thereon slidable in said one stepped bore, said flange means beingnormally positioned in non-restricting rel-ation with said orificemeans, passage means in said valve means between said inlet chamber andsaid one stepped bore, means for continuously flowing pressure fluidfrom said inlet chamber to said outlet chamber through said passagemeans, said one stepped bore and said orifice means, said Ithrottiingmeans being movable relative to said piston means to position saidflange means in flow restricting relation with said orifice means toestablish a pressure differential between said inlet and youtletchambers and energize said piston and the work producing end thereof,the established pressure differential also acting on said ange means to`oppose subsequent movement of said throttling means.

References Cited in the ile of this patent UNITED STATES PATENTS2,059,082 Brady et al. ct. 27, 1936 2,464,367 Balogh et al Mar. 15, 19492,544,042 Pontius Mar. 6, 1951 2,844,941 Ayers July 29, 1958

1. IN A POWER HYDRAULIC SERVO MOTOR COMPRISING A HOUSING HAVING A BOREWITH A PISTON ASSEMBLY THEREIN MOVABLE IN A WORK PRODUCING DIRECTION, AVARIABLE ORIFICE IN SAID PISTON ASSEMBLY THROUGH WHICH PRESSURE FLUID ISCONTINUOUSLY CIRCULATED, THROTTLING MEANS MOVABLE RELATIVE TO SAIDPISTON ASSEMBLY TO REDUCE THE SIZE OF SAID VARIABLE ORIFICE ANDESTABLISH A PRESSURE DIFFERENTIAL TO EFFECT MOVEMENT OF SAID PISTONASSEMBLY IN THE WORK PRODUCING DIRECTION, AND FLANGE MEANS ON SAIDTHROTTLING MEANS RESPONSIVE TO THE ESTABLISHED PRESSURE DIFFERENTIAL TOREDUCE THE SIZE OF SAID VARIABLE ORIFICE.